Electrophoretic and FPLC Analysis of Soluble Proteins in Four Portuguese Wines

Abstract

Two different methodologies were utilized to compare, analyze, and fractionate the soluble proteins of four Portuguese white wines made from Arinto, Bical, Fernão Pires, and Vital grape varieties. First, a new, simple, rapid and sensitive methodology consisting of a desalting step (5 min) of the wine under investigation, to remove salts and other low molecular mass contaminants which may interfere with the proteins during the analytical procedures, and a fractionation step (15 min) involving ion exchange fast protein liquid chromatography (FPLC): anion exchange chromatography on the Mono Q column of the FPLC, previously equilibrated with 50 mM ethanolamine buffer, pH 9.5, or cation exchange chromatography on the Mono S column of the FPLC, previously equilibrated with 50 mM formate buffer, pH 3.5, using suitable, continuous salt gradients to elute the wine proteins. This methodology is rapid (20 min), does not require prior concentration or purification of the proteins (which, besides being time consuming, may cause modification or denaturation of the proteins), and has the additional advantage of allowing the recovery of the isolated proteins in their native form. Second, polyacrylamide gel electrophoresis performed under reducing, denaturing conditions, followed by silver staining. This technique allows the estimation of molecular masses. The wines contained polypeptides with molecular masses ranging from 15.5 to 69 kDa. However, only six polypeptides were common to all four wines, namely the 15.5, 17, 20, 21.5, 24.5, and 69 kDa polypeptides. Both methods are sensitive, but the electrophoresis-based technique gives a higher resolution, is time consuming, destructive and more complex to perform. In contrast, the FPLC technique is non-destructive and very simple and rapid to perform.